1. Field of the Invention
The present invention is related to a power amplifier integrated circuit, and more particularly, to a power amplifier integrated circuit with compensation mechanism for temperature and output power.
2. Description of the Prior Art
In recent years, power amplifier integrated circuits (PAICs) have been widely used in various wired or wireless communication devices. Reference is made to FIG. 1 for a functional diagram illustrating a prior art PAIC 100. The PAIC 100 includes a plurality of connecting ports 101a-101c, n stage amplifying units OP1-OPn, and a bias circuit 110. The input port 101a is for receiving a radio frequency (RF) input signal RFin, the output port 101b is for providing an RF output signal RFout, and the supply voltage input port 101c is for receiving a bias voltage Vc. The bias circuit 110 includes n current sources for providing constant operational currents IS1-ISn to the n stage amplifying units OP1-OPn, respectively. Each of the n stage amplifying units OP1-OPn includes a bipolar junction transistor (BJT) having a collector coupled to the supply voltage input port 101c for receiving the bias voltage Vc and a base coupled to the bias circuit 110 for respectively receiving the operational currents IS1-ISn. The signal gains provided by the amplifying units OP1-OPn are represented by gm1*gm2 * . . . *gmn, respectively. Therefore, the overall signal gain of the PAIC 100 can be represented by a or RFout=(gm1*gm2 * . . . *gmn) RFin. Since the characteristics of BJTs are temperature-sensitive, the signal gains gm1-gmn may vary due to temperature fluctuations, and the RF output signal RFout may not be able to remain constant. On the other hand, when the RF output signal RFout fluctuates due to some reason, the prior art PAIC 100 is unable to provide compensation.
Reference is made to FIG. 2 for a functional diagram illustrating another prior art PAIC 200. The PAIC 200 includes a plurality of connecting ports 201a-201c, n stage amplifying units OP1-OPn, a bias circuit 210, a thermal-sensing circuit 220, and a feedback circuit 230. The input port 201a is for receiving an RF input signal RFin, the output port 201b is for providing an RF output signal RFout, and the supply voltage input port 201c is for receiving a bias voltage Vc. The thermal-sensing circuit 220 can detect variations in the operational temperature, thereby generating a corresponding thermal sensing signal St. The feedback circuit 230 can detect power variations of the RF output signal RFout, thereby generating a corresponding power compensation signal Sp. The bias circuit 210 includes n current sources for respectively providing operational currents IS1-ISn to n stage amplifying units OP1-OPn according to the thermal sensing signal St and the power compensation signal Sp. Each of the n stage amplifying units OP1-OPn includes a BJT having a collector coupled to the supply voltage input port 201c for receiving the bias voltage Vc and a base coupled to the bias circuit 210 for respectively receiving the operational currents IS1-ISn. The signal gains provided by the amplifying units OP1-OPn are represented by gm1-gmn, respectively. In the prior art PAIC 200, the variations in the operational temperature can be detected by the thermal-sensing circuit 220 and the variations in the RF output signal RFout can be detected by the feedback circuit 230. By adjusting the operational currents IS1-ISn accordingly, the signal gains gm1-gmn of the amplifying units OP1-OPn can thus be adjusted so as to compensate temperature or power fluctuations. However, the signal gains gm1-gmn can only be slightly modified by changing the operational currents IS1-ISn. The output power of the RF output signal RFout provided by the prior art PAIC 200 cannot be effectively stabilized.
Reference is made to FIG. 3 for a functional diagram illustrating another prior art PAIC 300. The PAIC 300 includes a plurality of connecting ports 301a-301c, n stage amplifying units OP1-OPn, a bias circuit 310, a thermal-sensing circuit 320, a feedback circuit 330, and a regulator 340. The input port 301a is for receiving an RF input signal RFin, the output port 301b is for providing an RF output signal RFout, and the supply voltage input port 301c is for receiving the RF output signal RFout. The thermal-sensing circuit 320 can detect variations in the operational temperature, thereby generating a corresponding thermal sensing signal St. The feedback circuit 330 can detect power variations in the RF output signal RFout, thereby generating a corresponding power compensation signal Sp. The bias circuit 310 includes n current sources for respectively providing constant operational currents IS1-ISn to n stage amplifying units OP1-OPn. The regulator 340 can generate a bias voltage Vc according to the thermal sensing signal St and the power compensation signal Sp. Each of the n stage amplifying units OP1-OPn includes a BJT having a collector coupled to the regulator 340 for receiving the bias voltage Vc and a base coupled to the bias circuit 310 for respectively receiving the operational currents IS1-ISn. The signal gains provided by the amplifying units OP1-OPn are represented by gm1-gmn, respectively. In the prior art PAIC 300, the variations in the operational temperature can be detected by the thermal-sensing circuit 320 and the variations in the RF output signal RFout can be detected by the feedback circuit 330. By adjusting the bias voltage Vc accordingly, the signal gains gm1-gmn of the amplifying units OP1-OPn can thus be adjusted so as to compensate temperature or power fluctuations. However, the signal gains gm1-gmn can only be slightly modified by changing the bias voltage Vc. The output power of the RF output signal RFout provided by the prior art PAIC 300 cannot be effectively stabilized.